Method for forming thin film on synthetic resin and multilayer film

ABSTRACT

An object of the invention, in the formation of a thin film on a synthetic resin, is to improve adhesiveness between the synthetic resin and the thin film by a relatively simple method. In the invention, a protective metallic layer is formed on a synthetic resin, and one thin film of (1) a semi-transmitting metallic mirror, (2) a total reflection metallic mirror, or (3) a transparent conductive film is formed. The material of the protective metallic layer is preferably selected from the group of Ti, Zr, Nb, Si, In, and Sn, and for sake of ensuring adhesiveness between the synthetic resin and the thin film, the film thickness of the protective metal layer is preferably 1 nm or more. Also, when the film thickness of the protective metallic layer is large, transmittance of the whole of the laminated film is lowered due to light absorption by the protective metallic layer, and hence, the film thickness of the protective metallic layer is preferably not more than 5 nm.

TECHNICAL FIELD

The present invention relates to a method of forming a thin filmcomposed of a metallic film, a conductive film, etc. on a syntheticresin with good adhesiveness and a laminated film obtained by thatmethod, which is made of a synthetic resin and a thin film.

BACKGROUND ART

When a thin film composed of a metallic film, a conductive film, etc. isformed on a synthetic resin composed of an electrode film-forming colorfilter for color display device, for the sake of ensuring adhesion ofthe thin film to the synthetic resin, a measure in which the surface ofthe synthetic resin is ionically irradiated prior to the formation ofthe thin film, thereby carbonizing a part of the surface of thesynthetic resin to improve the adhesion to the thin film (hereinafterreferred to “ionic cleaning process”) is known by the inventiondescribed in JP-A-10-10518 and so on.

Also, for the sake of forming a metallic film on a synthetic resin withgood adhesiveness, there is known a method in which particles of aphotocatalyst to decompose a synthetic resin to be used are carried onthe synthetic resin, irradiated with ultraviolet rays, and then cleanedin water while imparting ultrasonic vibration, and after removing theparticles of the photocatalyst on the foregoing surface, the resultingsurface is subjected to sputtering, vacuum deposition, or electrolessplating to coat a metallic film (JP-A-2001-11644).

In addition, in manufacturing optical information media such as laservideodiscs, there is a method in which a dilute gas is introducedbetween an anode installed with a synthetic resin substrate and acathode as a counter electrode, a direct voltage of from 1,000 to 2,500V is applied between the both electrodes, thereby generating plasma forfrom 1 to 20 seconds to preliminarily treat the surface of the resinsubstrate, and the surface of the synthetic resin substrate issubsequently subjected to sputtering to form a metallic reflecting film(JP-A-7-201087).

Since the foregoing ionic cleaning process involves a problem such thatwhen the surface of the synthetic resin is excessively carbonized, theadhesiveness of the thin film is inversely lowered, this process isnarrow in the range of the optimum condition for the carbonizationtreatment and is a hardly controllable technology.

That is, in the ionic cleaning process, the outermost surface of thesynthetic resin is carbonized by ion irradiation. However, when treatedexcessively, the synthetic resin is physically and chemically damaged,and hence, adhesiveness between the synthetic resin and the thin film islowered.

Also, the method in which the surface of the synthetic resin substrateis subjected to a combined treatment of ultraviolet treatment andultrasonic treatment and a plasma treatment, and a thin film such as ametallic film is subsequently formed on the surface of the syntheticresin substrate by sputtering, etc. is a large-scale method regardingthe preliminary treatment of the surface of the synthetic resinsubstrate and is not economical.

A problem of the invention is to provide a method of improving adhesionbetween a synthetic resin and a thin film by a relative simple methodand a laminated film obtained by that method, which is made of asynthetic resin and a thin film.

DISCLOSURE OF THE INVENTION

The foregoing problem of the invention is attained by the followingconstruction of the invention.

-   -   (1) A method of forming a thin film on a synthetic resin, which        comprises: a step of forming a protective metallic layer on a        synthetic resin; and a step of forming one thin film of a        semi-transmitting metallic mirror, a total reflection metallic        mirror, and a transparent conductive film on the formed        protective metallic layer.    -   (2) The method of forming a thin film on a synthetic resin        according to the above item (1), wherein the protective metallic        layer contains at least one of Ti, Zr, Nb, Si, In, and Sn.    -   (3) The method of forming a thin film on a synthetic resin        according to the above item (1), whrerein the protective        metallic layer is formed on the synthetic resin by sputtering.    -   (4) The method of forming a thin film on a synthetic resin        according to the above item (1), wherein the thin film is formed        on the protective metallic layer by sputtering.    -   (5) A laminated film comprising a protective metallic layer and        one thin film of a semi-transmitting metallic mirror, a total        reflection metallic mirror and a transparent conductive film, on        a synthetic resin layer.    -   (6) The laminated film according to the above item (5), wherein        the protective metallic layer contains at least one of Ti, Zr,        Nb, Si, In, and Sn.    -   (7) The laminated film according to the above item (5), wherein        the protective metallic layer has a film thickness of from 1 nm        to 5 nm.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view in the case where an oxide film is formed ona protective metallic layer of the invention.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   1: Synthetic resin    -   2: Protective metallic layer    -   2′: Oxide layer    -   3: Oxide film

BEST MODE FOR CARRYING OUT THE INVENTION

The foregoing problem of the invention can be solved by forming aprotective metallic layer on a synthetic resin by sputtering.

As the synthetic resin of the invention, are enumerated the followingthree kinds.

-   -   (1) Light scattering synthetic resin film    -   (2) Overcoat on CF (color filter)    -   (3) Plastic substrate

Examples of the foregoing light scattering synthetic resin film (1)include ones in which a light scattering synthetic resin is coated on aglass substrate; and examples of the overcoat on CF (color filter) (2)include ones in which a reflection film, a color filter, and an overcoatare successively laminated on a glass substrate. Also, the plasticsubstrate (3) is a non-surface treated plastic substrate itself.

The light scattering synthetic resin is one in which, for example, anacrylic photocurable resin is used as the material, and unevennesses areformed on the surface by a photo-litho process to have a lightscattering function.

The color filter is one that is generally formed by a “pigmentdispersion process” or a “printing process”, and in which the rawmaterial thereof is a natural high-molecular weight compound such asgelatin, casein, and glue, or a synthetic resin such as acrylic resins.Also, for the overcoat, synthetic resins such as acrylic based, epoxybased, and polyimide based resins are used as the material, and theovercoat is formed on the color filter for the purpose of protecting thecolor filter.

Examples of the plastic substrate include acrylic, epoxy based, andpolyimide based substrates.

Also, examples of the thin film to be formed on the protective metalliclayer include:

-   -   (1) A semi-transmitting metallic mirror (transmitting        performance is important);    -   (2) A total reflection metallic mirror; and    -   (3) A transparent conductive film (transmitting performance is        important).

Examples of the foregoing semi-transmitting metallic mirror (1) includeones in which a silicon oxide film, an aluminum film, and a siliconoxide film are successively laminated. Examples of the total reflectionmetallic mirror (2) include ones in which a silicon oxide film, analuminum film, and a silicon oxide film are successively laminated. Adifference between the forgoing (1) and (2) resides in film thickness ofthe metallic mirror and in whether or not light can transmittherethrough. Examples of the transparent conductive film include onesin which an indium oxide film is formed on a silicon oxide film.

In (1) and (3), the reasons why “transmitting performance is important”reside in the matter that in the case of semi-transmitting mirror, whena liquid crystal is brightly displayed by transmitting a backlight lightsource, the transmitting performance greatly influences lightness of thescreen display; and that in the case of transparent conductive film, inorder to display a liquid crystal, it is required to transmit light.

In the invention, for example, the protective metallic layer is formedon the surface of the synthetic resin by sputtering, thereby improvingadhesion between the synthetic resin and the thin film.

By forming the protective metallic layer made of, as a material, a metalthat is readily oxidized on the synthetic resin by sputtering,adhesiveness between the thin film formed as a film on the syntheticresin and the oxidized protective metallic layer increases, resulting inan improvement of the adhesiveness between the synthetic resin and thethin film. At this time, it is necessary to use a metal having goodadhesiveness to the synthetic resin as the protective metallic layermaterial.

The material of the protective metallic layer is selected from Ti, Zr,Nb, Si, In, and Sn, and for the sake of ensuring the adhesivenessbetween the synthetic resin and the thin film, the protective metalliclayer is required to have a film thickness of 1 nm or more. Also, whenthe film thickness of the protective metallic layer is large,transmittance of the whole of the laminated film is lowered due to lightabsorption by the protective metallic layer. Accordingly, the filmthickness of the protective metallic layer is required to be not morethan 5 nm.

The laminated film in which the thin film is formed on the syntheticresin via the protective metallic layer is used in electrodefilm-forming color filters for color display device, optical informationmedia such as laser videodiscs, and the like.

(Action)

Mechanism of the improvement in the adhesiveness of the invention isassumed to reside in the following one. That is, oxygen plasma generatedduring forming the thin film such as an oxide film oxidizes and degradesthe surface of the synthetic resin, whereby the adhesiveness between thethin film and the synthetic resin is lowered. However, by subjecting theprotective metallic layer to film formation on the surface of thesynthetic resin, the protective metallic layer prevents oxidation anddegradation of the synthetic resin by oxygen plasma, whereby theadhesiveness between the thin film and the synthetic resin is improved.

Also, as shown in FIG. 1, a protective metallic layer (such as a Tilayer) 2 on a synthetic resin 1 is oxidized when an oxide film (such asan SiO₂ film) 3 is subjected to film formation thereon. During this,since the film is very thin, the whole of the protective metallic layer2 is oxidized to become an oxide layer (such as a TiO₂layer) 2′. Forthisreason, since light absorption by the protective metallic layer 2 can beignored, it is possible to ensure transmitting characteristics of thethin film to be formed thereon.

From the foregoing results, in the case where the oxide film 3 such asan SiO₂ film is formed on the surface of the synthetic resin 1 bysputtering, etc., it is considered that the reason why film separationoccurs so far between the synthetic resin 1 and the oxide film 3 residesin the oxidation and degradation of the surface of the synthetic resinby oxygen plasma.

The mode for carrying out the invention will be described.

EXAMPLE 1

In this Example 1, an acrylic organic resin is used as a syntheticresin, and a total reflection aluminum mirror is formed as a thin filmon the surface of the synthetic resin.

The construction of a film to be laminated is comprised of glassplate/synthetic resin film/Ti film/SiO₂ film/Al film/SiO₂ film.

Here, an alkali-free glass was used as a glass substrate, polymethylmethacrylate as an acrylic photocurable resin was coated on the glasssubstrate by spin coating, and after baking at 200° C. for one hour, anuneven shape was formed on the surface by a photo-litho process. On theresulting surface, were successively formed a Ti film (film thickness:2.5 nm), an SiO₂ film (film thickness: 10 nm), an Al film (filmthickness: 90 nm), and an SiO₂ film (film thickness: 25 nm) bysputtering.

The sputtering condition of the Ti film is 2 Pa for pressure(introduction of only Ar gas) and 0.3 kW for discharge electric power(dynamic rate: 1.1 nm·m/min).

The sputtering condition of the SiO₂ film is 0.6 Pa for pressure (gascomposition: Ar/O₂=2/1) and 1.4 kW for discharge electric power (dynamicrate: 2.1 nm·m/min).

The sputtering condition of the Al film is 0.3 Pa for pressure(introduction of only Ar gas) and 4.1 kW for discharge electric power(dynamic rate: 37.8 nm·m/min).

COMPARATIVE EXAMPLE 1

In this Comparative Example, a total reflection aluminum mirror isformed as a thin film on the surface of a synthetic resin in the samemanner as in the foregoing Example 1.

The construction of a film to be laminated is comprised of glassplate/synthetic resin film/SiO₂ film (film thickness: 10 nm)/Al film(film thickness: 90 nm)/SiO₂ film (film thickness: 25 nm), and thesurface of the synthetic resin was carbonized immediately before filmformation of SiO₂ as a substrate by an ionic cleaning process under thefollowing condition.

The ionic cleaning condition of the synthetic resin film is as follows:

-   -   Pressure: 4 Pa, gas composition: Ar/O₂=100/1, discharge electric        power: 1.0 kW (RF), one minute, used target: SiO₂ (cathode).

The formation method of SiO₂ film (film thickness: 10 nm)/Al film (filmthickness: 90 nm)/SiO₂ film (film thickness: 25 nm) is the same as inExample 1.

The results of adhesiveness test of the laminated films obtained in theforegoing Example 1 (using Ti layer) and Comparative Example 1(conventional technology) are shown in Table 1. TABLE 1 Immediatelyafter film After warm After heating formation water test test Example 1∘ ∘ ∘ Comparative ∘ x x Example 1∘: No peeling occurs.Δ: Peeling occurs in less than 5 cells.x: Peeling occurs in 5 or more cells.

As is clear from the results of Table 1, it is noted that in Example 1,the Ti film is present so that the adhesiveness between the syntheticresin layer and the total reflection aluminum mirror is improved ascompared with Comparative Example 1.

EXAMPLE 2

In this Example, an overcoat on a color filter is used as a syntheticresin, and an ITO film as a transparent conductive film is formed as athin film on the surface of the foregoing synthetic resin.

The construction of a film to be laminated is comprised of glassplate/CF/overcoat (synthetic resin) film/Ti film/SiO₂ film/ITO film.

Here, an alkali-free glass was used as a glass substrate, and a colorfilter made of gelatin was formed on the glass substrate by a printingprocess to form a color filter-provided substrate. Trimelletic anhydrideas a curing agent was added to polyglycidyl methacrylate as an acrylicorganic resin, and the mixture was coated on the foregoing colorfilter-provided substrate by spin coating, followed by baking at 200° C.for one hour. On the resulting surface, were successively formed a Tifilm (film thickness: 2.5 nm), an SiO₂ film (film thickness: 10 nm), andan ITO film (film thickness: 200 nm) by sputtering.

The sputtering condition of the Ti film is 2 Pa for pressure(introduction of only Ar gas) and 0.3 kW for discharge electric power(dynamic rate: 1.1 nm·m/min).

The sputtering condition of the SiO₂ film is 0.6 Pa for pressure (gascomposition: Ar/O₂=2/1) and 1.4 kW for discharge electric power (dynamicrate: 2.1 nm·m/min).

The sputtering condition of the ITO film is 0.3 Pa for pressure (gascomposition: Ar/O₂=99/1) and 5.5 kW for discharge electric power(dynamic rate: 32.4 nm·m/min).

COMPARATIVE EXAMPLE 2

In this Comparative Example 2, an ITO film is formed as a thin filmdirectly on an overcoat on CF in the same manner as in the foregoingExample 2.

The construction of a film to be laminated is comprised of glassplate/CF/overcoat (synthetic resin) film/SiO₂ film (film thickness: 10nm)/ITO film (film thickness: 200 nm), and the surface of the syntheticresin was carbonized immediately before film formation of SiO₂ as asubstrate by an ionic cleaning process under the following condition.

The formation method of SiO₂ film (film thickness: 10 nm)/ITO film (filmthickness: 200 nm) is the same as in Example 2.

The ionic cleaning condition of the synthetic resin film is as follows:

Pressure: 4 Pa, gas composition: Ar/O₂=100/1, discharge electric power:1.0 kW (RF), one minute, used target: SiO₂ (cathode).

The results of adhesiveness test of the laminated films obtained in theforegoing Example 2 (using Ti layer) and Comparative Example 2(conventional technology) are shown in Table 2. TABLE 2 Immediatelyafter film After warm After heating formation water test test Example 2∘ ∘ ∘ Comparative ∘ x x Example 2∘: No peeling occurs.Δ: Peeling occurs in less than 5 cells.x: Peeling occurs in 5 or more cells.

As is clear from the results of Table 2, it is noted that in Example 2,the Ti film is present so that the adhesiveness between the syntheticresin layer (overcoat on CF) and the ITO film is improved as comparedwith Comparative Example 2.

EXAMPLE 3

The ground of setting the film thickness of the protective metalliclayer of the invention will be described with reference to an example ofusing Ti as the protective metallic layer.

(1) A lower limit value of the film thickness of the protective metalliclayer was set by changing the film thickness and confirming adhesivenessbetween the synthetic resin film and the thin film. The results areshown in Table 3. TABLE 3 Set film thickness (nm) 0.5 1 3 5 10Immediately Δ ∘ ∘ ∘ ∘ after film formation After warm x ∘ ∘ ∘ ∘ watertest After heating x ∘ ∘ ∘ ∘ test*: The sputtering condition was the same as the condition of Example 1.*: The film construction was the same as in “total reflection Al mirror”of Example 1.*: The film thickness wad adjusted by discharge electric power.

Here, the film construction and the sputtering condition of the Ti filmwere the same as in Example 1. Also, the film thickness of the Ti filmshown in Table 3 was adjusted by discharge electric power.

(2) An upper limit value of the film thickness of the protectivemetallic layer was set by changing the film thickness and confirmingoptical characteristics of the resulting laminated film. The results areshown in Table 4. TABLE 4 Set film thickness (nm) 0 1 3 5 6 10Absorbance 23.0 23.0 23.0 23.0 28.3 35.9 (%) Judgment — OK OK OK OK OK*: Film construction, Glass/Ti/SiO₂/Al/SiO₂ (10/8/25) :semi-transmitting Al mirror

Here, the sputtering condition of the Ti film was the same as inExample 1. Also, the film thickness of the Ti film shown in Table 4 wasadjusted by discharge electric power.

As described above, it is noted that in the case where it is demanded toensure only the adhesiveness, there is a lower limit in the filmthickness of the protective metallic film, whereas in the case where oneattaches importance to adhesiveness and transmittance, there is an upperlimit in addition to the lower limit; and it has become clear that whenthe film thickness of the Ti film falls within the range of from 1 nm to5 nm, satisfactory results are revealed with respect to the adhesivenessand light absorbance.

The evaluation methods for the adhesiveness performed in the foregoingExamples and Comparative Examples are shown below.

The glass substrate having formed thereon the laminated film to beevaluated is evaluated by crosscutting and peeling immediately after thefilm formation and after the weather resistance test.

(a) Crosscutting:

The film surface is cut with 11 lines at an interval of 1 mm in each ofthe longitudinal and lateral directions and separated into pieces eachhaving a size of 1 mm-square. Thus, 100 cells of 1 mm-square areprepared.

(b) Peeling:

After crosscutting, a cellophane adhesive tape (NITTO No. 29) is stuckon the film surface and then peeled apart at right angles while puttingsome snap, and a peeled portion is visually confirmed.

(c) Weather Resistance Test:

-   -   (1) Warm water test: The substrate is dipped in warm water of        80° C. for 30 minutes.    -   (2) Heating rest: The substrate is baked in the air at 240° C.        for one hour.

Industrial Applicability

According to the invention, it is possible to improve adhesivenessbetween a synthetic resin and a thin film and to maintain theadhesiveness of the thin film even when passing through a sever process(at high temperatures and in acid or alkaline solutions).

1. A method of forming a thin film on a synthetic resin, whichcomprises: a step of forming a protective metallic layer on a syntheticresin; and a step of forming one thin film of a semi-transmittingmetallic mirror, a total reflection metallic mirror, and a transparentconductive film on the formed protective metallic layer.
 2. The methodof forming a thin film on a synthetic resin according to claim 1,wherein the protective metallic layer contains at least one of Ti, Zr,Nb, Si, In, and Sn.
 3. The method of forming a thin film on a syntheticresin according to claim 1, whrerein the protective metallic layer isformed on the synthetic resin by sputtering.
 4. The method of forming athin film on a synthetic resin according to claim 1, wherein the thinfilm is formed on the protective metallic layer by sputtering.
 5. Alaminated film comprising a protective metallic layer and one thin filmof a semi-transmitting metallic mirror, a total reflection metallicmirror and a transparent conductive film, on a synthetic resin layer. 6.The laminated film according to claim 5, wherein the protective metalliclayer contains at least one of Ti, Zr, Nb, Si, In, and Sn.
 7. Thelaminated film according to claim 5, wherein the protective metalliclayer has a film thickness of from 1 nm to 5 nm.